The present invention relates broadly to an RF modulator apparatus, and in particular to a microprocessor-controlled RF modulator apparatus.
The state of the art of radar target signal simulators is well represented and alleviated to some degree by the prior arts apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,571,479 issued to Horattas et al on Mar. 16, 1971; PA0 U.S. Pat. No. 3,783,172 issued to Bernstein on Jan. 1, 1974; PA0 U.S. Pat. No. 3,792,475 issued to Smetana on Mar. 9, 1972; PA0 U.S. Pat. No. 4,168,502 issued to Susie on Mar. 15, 1978; PA0 U.S. Pat. No. 4,224,583 issued to Larken on Nov. 29, 1978; and PA0 U.S. Pat. No. 4,327,417 issued to Zaczek on June 6, 1980.
The early prior art approach to radar target generation or simulation is shown in the prior art patents of Horattas et al and Bernstein. The Horattas et al patent is directed toward a digital electronic target generator wherein digitized radar targets are stored in a memory matrix where range is "bit" oriented and aximuth is "word" oriented. Each word in the matrix represents an azimuth line segment of a target on a radar display and the bit position within a matrix word represents the target range, each bit being the smallest range unit defined by the resolution of the display. A computer identifies the location of all targets in the display matrix and transfers the data to parallel-to-serial shift registers which output serial pulse trains representative of the target words. An output signal having analog characteristics is produced by summing the shift register output results and may be used in a simulator visual display.
The Berstein patent comprises a radar simulator apparatus which utilizes a general-purpose digital computer and a special interface which generates suitable video signals in response to the computer outputs to drive a radar set. In a radar simulator in which several different types of radar targets are simulated, the apparatus of this invention is used to generate the video signals which will display a plurality of mobile targets on the radar set. A limited number of such targets are displayed, and the characteristics of these targets are entered into the computer. Information representing the initial locations of the selected targets and their directions and speeds of movement is inserted into the computer from a remote station, and the computer performs the necessary navigational computations to continually determine the location of the radar set in the gaming area, the bearing of each of the targets from the radar set, and the bearing of the radar antenna at any time. The ranges of all of the targets on a particular bearing are entered by the computer into a register in the order of increasing range from the radar set. When the simulated radar antenna bearing agrees with the target bearing, the stored target ranges are read from the register and are converted into video signals to drive the radar set.
The Smetana, Zaczek and Susie patents respectively illustrate the present day approach of prior art target signal simulators which have been either extremely complicated in that they were controlled by a digital computer or limited to producing signals useful in testing short range or low PRF radar systems. The computer based systems were complicated due to the extensive programming which is required to generate the delays that correspond to the range of the simulated target and to calculate the pulse repetition frequency of the simulated target signal. The limited range of the simulators which did not use digital computers, resulted primarily from the fact that they provided no convenient means for generating a simulated target signal in which the time interval between adjacent pulses of the signal was less than the transit time to and from the simulated target.
The Larkin patent presents another novel approach to the field of radar target signal simulation through the use of a linear attenuator which uses a dc control current to change the RF resistance of PIN diodes that are in series and parallel with the load. As the control current changes, the RF resistance of the series diode will vary inversely, while the RF resistance of the parallel diode will vary directly thereby providing attenuation which changes linearly as a function of the control current through the series diode. The present invention is directed to a microprocessor-controlled RF modulator apparatus which provides RF target return signals to a fire control radar with realistic radar characteristics.